A DNA array sensor utilizing magnetic microbeads and magnetoelectronic detection

Magnetic bead handling on-chip: new opportunities for analytical applications

“…A research group at the Naval Research Laboratory, Washington DC (Baselt et al 1998;Edelstein et al 2000;Miller et al 2001;Rife et al 2003), followed by others (Coehoorn and Prins 2003;Graham et al 2003), have developed a microsystem for the capture and detection of micron-sized, paramagnetic beads on a chip containing an array of GMR sensors, the so-called bead array counter (BARC). The BARC is based on a sandwich assay, where the target molecule is bound to an immobilized probe on the GMR sensor, after which, the magnetic label is bound to the target using specific ligand-receptor interactions.…”

“…To maximize the sensor response, the magnetic beads should have a magnetization as high as possible, and yet, remain non-remnant to avoid clustering when suspended in solution. With the goal of achieving larger signals from the magnetic labels, soft ferromagnetic beads with 100% magnetic content and a much higher saturation magnetization have been developed (Miller et al 2001). NiFe beads of 1-lm diameter showed a susceptibility of $3, the maximum obtainable value for a uniformly magnetized sphere.…”

Magnetoresistive biochips

“…Fluorophore labels are replaced by magnetic labels (superparamagnetic particles), and detection is done using an integrated magnetic field sensor (GMR multilayer [6], spin valve [7],AMR r.ing [8], Hall effect cross [9]). The hybridization detection process is shown in Fig.1b.…”

“…For example consider Ilm size labels. If a linear response to the number of labels (up to few hundred) is required, as for example in a gene expression chip, the sensor can be made of a spin valve or GMR material in a meander configuration occupying most of the area under the probe pad [6,11]. The output is proportional to the area of the sensor excited by the particles fringe fields.…”

Continuous-flow ferrohydrodynamic sorting of particles and cells in microfluidic devices

“…The label-based methods are manually intensive and time-consuming. The magnetic moments of these beads, even from the same batch, can vary dramatically due to their manufacturing procedure, making scaling of the method scaling difficult (Hafeli et al 1997;Miller et al 2001;Rife et al 2003;Mihajlovic et al 2007;Shevkoplyas et al 2007).…”